The present invention relates to flow control valves.
Conventional flow control devices comprise, for example, a spindle having a handle at its upper end, a disk and an externally threaded portion in screw-thread engagement with an internally threaded portion of a case having a disk seat therein. The disk is pressed against the seat or moved away therefrom by rotating the handle to close or open a fluid channel extending through the case. On the other hand, so-called rotary valves are known as change-over valves or directional control valves. Such valves comprise a valve element having many fluid channels and rotatable so as to cause the desired one of the channels to communicate with an opening portion of the valve casing to effect change-over between flows.
However, the conventional flow control device described has the problem that the seal face of the disk becomes indented during long use, displacing the handle when the disk is closed, or that the disk closing position changes owing to a machining error involved in the fabrication of the device, consequently influencing the opening-closing operation of the device. It is likely that the operator will tighten up the handle excessively to produce an indentation in or cause damage to the seal face of the disk, thereby aggravating the above problem. With the conventional rotary valve as a change-over valve, it is not easy to make the valve element which has many fluid channels. Further use of the valve as a sanitary valve involves the problem that it is difficult to completely seal the fluid channels in the valve.